We propose to characterize excitation contraction coupling and its inhibition by Ca2+ antagonists (Cats) in the rabbit and rat aortae and mesenteric resistance arteries, and the rabbit coronary and basilar arteries. Our goal is to identify and explain the variable sensitivity to CAts displayed by agonist-and depolarization-induced contractions in various types of arteries. We postulated that arterial CAt selectivity is related to variable contributions by different Ca2+ entry pathways (passive leak, receptor operated channels (ROCs) and potential sensitive channels (PSCs)) and by intracellular Ca2+ release in delivering Ca2+ to the myoplasm. This hypothesis will be tested by measuring 45Ca influx into the different arterial cells during rest and activation by NE and high K-depolarization and, in selected cases, by stretch, serotonin, histamine, angiotension and a prostaglandin endoperoxide analogue, and during inhibition by the CAts nisoldipine, diltiazem and D600 and in selected cases by series of polyvalent cations, calmodulin antagonists and agents that raise intracellular cAMP. Membrane potentials and contractile tension will be measured in parallel experiments under identical conditions. These data will provide evidence for the nature of the smooth muscle Ca2+ entry processes, show why CAts are more effective in some cases than in others, and demonstrate how variable intracellular Ca2+ buffering can affect CAt potency. We have recently acquired the technique of primary culture of arterial smooth muscle cells and will employ it to obtain absolute values for cell Ca content, muoplasmic [Ca2+], and increases in Ca2+ permeability during activation and during its inhibition by CAts. Our long range goal is to characterize the various smooth muscle CA2+ channels and their inhibition by CAts by the patch clamp technique and to attempt quantitative correlations between the Ca2+ currents and 45 Ca fluxes.